The pumping chamber is comprised of two sets of rollers, shoes, and plungers, which rotate inside a cam ring. The cam ring has lobes for each injector on the inside.

The force of the fuel entering the pumping chamber with the centrifugal force produced by the spinning rotor part the plungers. The plungers move outward an amount directly proportional to the volume of fuel passed by the metering valve.

As the rotor turns, the cam ring lobes squeeze the rollers together and as a result, it pushes the rollers. As the plungers are pushed together, they pressurize fuel until the injectors nozzles open at their preset pop pressure.

The fuel at injection pressure is forced back along the centre passage of the rotor and into the discharge port and released when the discharge port lines up with an injector line outlet in the hydraulic head.

As the single discharge port rotates with the rotor it lines up with each of the hydraulic head injector line outlets in a sequence matching the engine’s firing order. Each injector outlet is connected to an injector nozzle by a high-pressure line. The injector pump varies the rate and quantity of fuel delivered to the nozzles as demanded by the throttle and/or governor.

A delivery valve, in the centre of the distributor rotor, assists the injector nozzles to rapidly reseat and prevents anatomized fuel from dribbling into the pre-combustion chambers. Pressurized fuel from the pumping chamber forces the delivery valve plunger slightly out of its bore so fuel flows past the plunger and then out the discharge port. When fuel pressure drops, the delivery valve plunger immediately reseats, causing a rapid drop in injection line pressure.

Housing pressure and transfer pump pressure behind the power piston influence the action of the servo piston. When the engine is cranking, the fuel behind the servo piston 8N7005 is at housing pressure, and the power piston is seated against the housing. As the engine speed increases, transfer pressure rises and the subsequent increase in transfer pump pressure forces fuel into a chamber behind the power piston.